We will investigate the clinical usefulness of the flow information available from humans by using quantitative Doppler ultrasonic instruments and techniques. The validity of the information will be checked by direct comparison with the information obtained by dye- contrast arteriography and by electromagnetic flowmeter measurements made in the operating room. Our major goal is to determine the conditions under which absolute volume flow, absolute velocity of flow, and true phasic flow waveforms can be obtained. The vessels chosen for investigation are the common, internal and external carotid arteries, and the vertebral arteries. The techniques we will employ will use apparatus we have already developed at the Institute. Specific transducer designs suitable for each application will be used. The Doppler techniques to be employed are: ultrasonic arteriography for determining the diameter of blood vessels transcutaneously for direct comparison with X-ray arteriography and use of the angular dependence of the Doppler frequency to determine transcutaneously the absolute velocity of blood flow in vessels. These techniques will be applied in conjunction with the clinical staff of Providence Hospital, Seattle, to determine the importance of the information derived to clinical management and decision making.